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 A287650 Number of doubly symmetric diagonal Latin squares of order 4n with a fixed first row. 5
 2, 12288, 81217160478720 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A doubly symmetric square has symmetries in both the horizontal and vertical planes. One plane symmetry requires one-to-one correspondence between the values of elements a[i][j] and a[N-i][j] in a vertical plane, and between the values of elements a[i][j] and a[i][N-j] in a horizontal plane for 1 <= i,j <= N. - Eduard I. Vatutin, Alexey D. Belyshev, Oct 09 2017 Belyshev (2017) proved that doubly symmetric diagonal Latin squares exist only for orders N == 0 (mod 4). LINKS A. D. Belyshev, Proof that the order of a doubly symmetric diagonal Latin squares is a multiple of 4, 2017 (in Russian) E. I. Vatutin, Discussion about properties of diagonal Latin squares at forum.boinc.ru, value a(4) is wrong (in Russian) E. I. Vatutin, Discussion about properties of diagonal Latin squares at forum.boinc.ru, corrected value a(4) (in Russian) E. I. Vatutin, S. E. Kochemazov, O. S. Zaikin, Estimating of combinatorial characteristics for diagonal Latin squares, Recognition — 2017 (2017), pp. 98-100 (in Russian) E. I. Vatutin, S. E. Kochemazov, O. S. Zaikin, On Some Features of Symmetric Diagonal Latin Squares, CEUR WS, vol. 1940 (2017), pp. 74-79. E. I. Vatutin, S. E. Kochemazov, O. S. Zaikin, V. S. Titov, Investigation of the properties of symmetric diagonal Latin squares, Proceedings of the 10th multiconference on control problems (2017), vol. 3, pp. 17-19 (in Russian) E. I. Vatutin, S. E. Kochemazov, O. S. Zaikin, V. S. Titov, Investigation of the properties of symmetric diagonal Latin squares. Working on errors, Intellectual and Information Systems (2017), pp. 30-36 (in Russian) FORMULA a(n) = A292517(n) / (4n)!. EXAMPLE Doubly symmetric diagonal Latin square example: 0 1 2 3 4 5 6 7 3 2 7 6 1 0 5 4 2 3 1 0 7 6 4 5 6 7 5 4 3 2 0 1 7 6 3 2 5 4 1 0 4 5 0 1 6 7 2 3 5 4 6 7 0 1 3 2 1 0 4 5 2 3 7 6 Reversion of all rows is equivalent to the exchange of elements 0 and 7, 1 and 6, 2 and 5, 3 and 4; hence, this square is horizontally symmetric. Reversion of all columns is equivalent to the exchange of elements 0 and 1, 2 and 4, 3 and 5, 6 and 7; hence, the square is also vertically symmetric. CROSSREFS Cf. A003191, A287649, A292517. Sequence in context: A134656 A128122 A082178 * A082912 A265013 A083973 Adjacent sequences:  A287647 A287648 A287649 * A287651 A287652 A287653 KEYWORD bref,nonn,more AUTHOR Eduard I. Vatutin, May 29 2017 EXTENSIONS a(2) corrected by Eduard I. Vatutin, Alexey D. Belyshev, Oct 09 2017 Edited and a(3) from Alexey D. Belyshev added by Max Alekseyev, Aug 23 2018, Sep 07 2018 STATUS approved

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Last modified October 16 20:34 EDT 2018. Contains 316275 sequences. (Running on oeis4.)